The number of pages in the document.
This must be set to a positive number before the rendering starts. It may be set in a signal@Gtk.PrintOperation::begin-print signal handler.
Note that the page numbers passed to the signal@Gtk.PrintOperation::request-page-setup and signal@Gtk.PrintOperation::draw-page signals are 0-based, i.e. if the user chooses to print all pages, the last ::draw-page signal will be for page @n_pages - 1.
Set nPages property.